Monsters (2010) is one of my favorite low budget films. Shot for half a million. Lots and lots of the things shot on location were later modified in post, like signage changed to have warnings about the alien quarantine zone.

"NASA discovered a few years ago the real possibility of alien life and consequently a probe was set up and launched in order to collect sample. After crashing during the re-entry over Central America, new life forms began to appear and spread rapidly. Half of Mexico is quarantined as an infected zone. In this context we follow the story of a US journalist escorting his bosses's daughter through this area to the United States."